Multiple rare-earth co-activated long-afterglow luminescent material

ABSTRACT

The present invention relates to a multiple rare earth co-activated long-afterglow luminescent material having its general chemical composition depicted by a formula aMO.bAl 2 O 3 .cSiO 2 .dGa 2 O 3 :xEu.yB.zN, wherein a, b, c, d, x, y, and z are coefficients with the ranges of 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦1, 0.0001≦z≦1, M is Ca or Sr, N is Dy or Nd, wherein Sr (or Ca), Al, Si, Ga are main matrix elements and Eu, B, Dy (or Nd) elements are activators. The long-afterglow luminescent material according to the present invention has advantage of a longer persistence period and a water resistance greatly superior to known rare-earth activated aluminate long-afterglow luminescent materials.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a long-afterglow luminescent material, and more particularly to a multiple rare-earth co-activated long-afterglow luminescent material having excellent luminescence properties and water resistance.

2. Description of Related Art

The long-afterglow phenomenon is called a noctilucent phenomenon in folksay, which has been known since ancient times. The famous “luminescent pearl”, and “luminescent wall” are just natural minerals of fluorite type, which can conserve the energy of sunlight on day and slowly emit energy in the form of luminescence at night, that is, noctilucence. A long-afterglow material is a kind of material that can converse the energy from outside light radiation such as ultraviolet light, visible light or the like, and then slowly emit the saved energy in the form of visible light at room temperature. The cause of the long-afterglow phenomenon is generally regarded as the appearance of the impurity energy level (defect energy level) due to doping. During the stage of excitation, the impurity energy level can capture vacancies or electrons. While the excitation is finished, these electrons or vacancies are set free due to the heat movement which can transfer the energy to an activated ion and cause it to glow. Because heat movement release of energy is slow, luminescence of an activated ion takes on the characteristic of long-afterglow luminescence. When the trap depth is too big, the captured electrons or vacancies will not successfully be released from the trap, which thus makes afterglow luminescence of the materials too weak. While the trap depth is too small, the release velocity of electrons and vacancies will be too big, which can shorten the afterglow period. Besides required suitable trap depth, it is also important for doped ions to have suitable affinity with electrons and vacancies in the trap. Neither too strong nor too weak affinity will prolong the afterglow.

The long-afterglow property of the materials is based on three following processes: (1) outside light energy can be conserved by the trap in the material, (2) the saved energy can be effectively transferred to luminescent ions, and (3) this energy must be released by way of radiant transition of luminescent ions, and not be extinct. Therefore, besides luminescent ions, other assistant activated elements play an important role in afterglow properties and characteristics of the materials.

In the prior art, there are two types as long-afterglow materials, namely sulfides denoted as ZnS:Cu and Eu²⁺ activated alkaline-earth metal aluminate MAl₂O₄ (M denoting alkaline-earth metals) rare-earth long-afterglow luminescent materials. Long-afterglow luminescent materials of ZnS:Cu have already been used for several decades, but these materials have a disadvantage—a relatively shorter afterglow period. To prolong the luminescent period, it is required to dope radioactive elements, for example Pm¹⁴⁷, Ra or the like, which would have a negative effect on the human body and environment. In addition, it can cause the following decomposing reaction: ZnS+H₂O→Zn+H₂S because of the cooperation of ultraviolet contained in sunlight and water in the air.

In recent years, compared with ZnS:Cu luminescent materials, the developed long-afterglow luminescent materials of Eu²⁺ activated alkaline-earth metal aluminate (Chinese Patent Application No. 91107337.X, U.S. Pat. Nos. 5,376,303 and 5,424,006, and Japanese Patent Application Publication Nos. 8-127772, 8-151573 and 8-151574) manifest higher luminescent brightness, longer afterglow life, and better stability, but their water resistance is poor. To overcome this shortcoming, the coated film treatment method is generally used, but this can increase the cost of the material and, at the same time, coated film can also inevitably influence the absorption and conservation of the outside light. In addition, although long-afterglow luminescent materials of silicate substrate developed in recent years have better water resistance, luminescent brightness and afterglow property are not good.

All references cited herein are incorporated herein by reference in their entireties.

BRIEF SUMMARY OF THE INVENTION

In a first aspect, the invention comprises a multiple rare-earth co-activated long-afterglow luminescent material, having a chemical composition depicted by the formula

aMO.bAl₂O₃ .cSiO₂ .dGa₂O₃ :xEu.yB.zN

wherein a, b, c, d, x, y and z are coefficients having ranges of 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦1, 0.0001≦z≦1; M is at least one of Ca, Sr elements and N is at least one of Dy and Nd elements.

In certain embodiments, in the chemical composition 0.8≦a≦1.2, 0.8≦b≦2, 0.002≦c≦0.061, 0.005≦d≦0.5, 0.005≦x≦0.1, 0.02≦y≦0.5, and 0.005≦z≦0.05.

In certain embodiments, in the chemical composition a=1, 1≦b≦2, 0.002≦c≦0.02, 0.005≦d≦0.01, 0.01≦x≦0.02, 0.05≦y≦0.3, 0.01≦z≦0.04.

In certain variants of the above embodiments, the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxides or hydrates of Aluminum; Si or Ga elements result from oxides of Silicon or Gallium; Eu, Dy, and Nd result from oxides or oxalates of Europium, Dysprosium or Neodymium; and B results from oxides of Boron or Boric acid.

In a second aspect, the invention comprises a method for manufacturing the multiple rare-earth co-activated long-afterglow luminescent material according to claim 1, comprising the following steps: (1) mixing the raw materials sufficiently according to the following molar ratio, and (2) sintering the resultant mixture for 2-6 hours under 1200˜1500° C. at a reductive atmosphere, whereby the resultant is obtained, wherein, MO:Al₂O₃:SiO₂:Ga₂O₃:Eu:B:N=a:b:c:d:x:y:z; and 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦1, 0.0001≦z≦1 are selected; M is Ca or Sr and N is Dy or Nd; Sources of the said raw materials are: the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxide or hydrate of Aluminum; Si or Ga elements, respectively, result from oxides of Silicon or Gallium; Eu, Dy, and/or Nd result from oxides or oxalates of europium, dysprosium or neodymium; and B results from oxides of Boron or Boric acid.

In certain embodiments of the method, the following parameters of the chemical composition ratio of each raw material are selected: a=1, 1≦b≦2, 0.002≦c≦0.02, 0.005≦d≦0.01, 0.01≦x≦0.02, 0.05≦y≦0.3, 0.01≦z≦0.04.

In certain embodiments of the method, said reductive atmosphere is CO or H₂ gas.

In a third aspect, the invention comprises a use of multiple rare-earth co-activated long-afterglow luminescent material as described above as a direction identifier for subway passengers, traffic signs, bridge identifiers, scutellate signs, border lines, walking passages, lamp posts, tunnel marks, fire control and emergency escape signs, ship decks, dock signs, and oil well signs. In certain embodiments, said multiple rare-earth co-activated long afterglow luminescent material can be used for dresses, aqueous inner and outer wall coatings, paints, and print inks.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph depicting a luminescent spectrum of long-afterglow for sample 3.

FIG. 2 is a graph depicting a luminescent spectrum of long-afterglow for sample 9.

FIG. 3 is a graph depicting a luminescent spectrum of long-afterglow for sample 15.

The above description of the present invention is further explained in detail by means of specific embodiments in the form of examples hereinafter, however, it should not be understood that the scopes of the above subject are limited by the following examples. Any modifications and variations based on the present invention should not depart from the scopes of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides a multiple rare-earth co-activated long-afterglow luminescent material having excellent luminescence properties and water resistance.

The chemical composition of the multiple long-afterglow luminescent material according to the present invention is depicted by the following formula:

aMO.bAl₂O₃.cSiO₂.dGa₂O₃:xEu.yB.zN, wherein a, b, c, d, x, y, and z are coefficients (molar ratio) with the ranges of 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦1, 0.0001≦z≦1; M is Ca or Sr; N is Dy or Nd, wherein Sr (or Ca), Al, Si, Ga are main matrix elements and Eu, B, Dy (or Nd) elements are activators.

In a preferred embodiment the composition is:

0.8≦a≦1.2, 0.8≦b≦2, 0.002≦c≦0.061, 0.005≦d≦0.5, 0.005≦x≦0.1, 0.02≦y≦0.5, 0.005≦z≦0.05.

The most preferable composition is:

A=1, 1≦b≦2, 0.002≦c≦0.02, 0.005≦d≦0.01, 0.01≦x≦0.02, 0.05≦y≦0.3, 0.01≦z≦0.04.

Among the raw materials used in the multiple rare-earth co-activated long afterglow luminescent material provided by the present invention, the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxide or hydrate of Aluminum; the Si or Ga elements result from oxides of Silicon or Gallium; Eu, Dy, and Nd result from oxides or oxalates of Europium, Dysprosium or Neodymium; B results from oxides of Boron or Boric acid.

The present invention further provides a method of manufacturing the above multiple rare-earth co-activated long-afterglow luminescent material comprising the following steps: (1) mixing the raw materials sufficiently according to the following molar ratio, and (2) sintering the resultant mixture for 2-6 hours under 1200˜500° C. at reductive atmosphere such as CO or H₂ gas.

The luminescent materials according to the present invention are obtained at a reductive atmosphere, wherein the Eu element exists in the form of a bivalence ion and its luminescence results from transition of 4f5d-4f. Because 5d electrons of Eu²⁺ are easy to be effected by a substrate environment, the luminescence of Eu²⁺ are changed with different substrates and emit visible light in the range from blue color to red color. The long-afterglow luminescent materials according to the present invention can be of green, cyan, and purple long-afterglow luminescence.

The substrate matrix according to the present invention can include SiO₂ and Ga₂O₃. Water resistance of the luminescent materials can be greatly improved thereby.

The present invention further provides the applications of the long-afterglow luminescent materials. With the excellent properties of the luminescent materials and water resistance, they can be expected to be used in a broad range of applications such as (1) direction identifiers for subway passengers, traffic signs, bridge identifiers, scutellate signs, border lines, walking passages, lamp posts, tunnel marks, or the like; (2) fire control and emergent escape signs; (3) ship decks, dock signs, and oil well signs; (4) special clothing (e.g., dresses), (5) aqueous wall coatings, paints and print inks used for various buildings.

The present invention, by selecting an element to be used as an activator, one can make long-afterglow materials have a suitable trap, and also optimize the process of energy transfer in the materials. Thereby, the efficiency of the transfer can be increased and the long-afterglow luminescent property of the material can be greatly improved. At the same time, the long-afterglow materials according to the present invention are of excellent water resistance with a luminescence period of more than 60 hours, which can maintain a better long-afterglow characteristic after dipping it in water for 60 hours, and taking advantage of excellent properties and broad applications.

The invention will be illustrated in more detail with reference to the following Examples, but it should be understood that the present invention is not deemed to be limited thereto.

EXAMPLES Examples 1-6

Preparation of green rare-earth long-afterglow luminescent materials

The molar ratio of raw materials for examples 1-6 are listed in Table 1.

TABLE 1 Mole ratio of raw materials in samples (mol) Samples SrCO₃ Al₂O₃ SiO₂ Ga₂O₃ Eu₂O₃ Dy₂O₃ H₃BO₃ 1 1 1 0 0 0.01 0.02 0 2 1 1 0 0 0.01 0.02 0.1 3 1 1 0.05 0.005 0.01 0.02 0.1 4 0.5 0.6 0.6 0.03 0.006 0.012 0.6 5 0.8 1.3 0.001 0.005 0.2 0.3 1 6 0.5 0.5 0.005 0.0001 0.0001 0.0001 0.0001

The manufacturing method includes mixing SrCO₃, Al₂O₃, SiO₂, Ga₂O₃, Eu₂O₃, Dy₂O₃ and H₃BO₃ according to the molar ratio listed in Table 1 and then sufficiently grinding and mixing by ball miller, reacting for 4 hours at about 1400° C. under the mixture gas of N₂ and H₂.

For raw materials in Table 1, when SrCO₃, Al₂O₃, Eu₂O₃, Dy₂O₃, H₃BO₃ are respectively replaced by SrO, Al(OH)₃, Europium oxalate, Dysprosium oxalate, B₂O₃, the green rare-earth long-afterglow luminescent materials of similar properties are obtained.

Examples 7-12

Preparation of cyan rare-earth long-afterglow luminescent materials according to the present invention.

The molar ratio of raw materials for examples 7-12 are listed in Table 2.

TABLE 2 Mole ratio of raw materials in samples (mol) Samples SrCO₃ Al₂O₃ SiO₂ Ga₂O₃ Eu₂O₃ Dy₂O₃ H₃BO₃ 7 1 1.8 0 0 0.012 0.03 0 8 1 1.8 0 0 0.012 0.03 0.2 9 1 1.8 0.06 0.01 0.01 0.03 0.2 10 0.6 1.1 0.6 0.03 0.006 0.012 0.6 11 1.6 3 0.001 0.005 0.1 0.3 1 12 2 3 1 1 1 1 1

The manufacturing method includes mixing SrCO₃, Al₂O₃, SiO₂, Ga₂O₃, Eu₂O₃, Dy₂O₃ and Boric Acid according to the molar ratio listed in Table 2 and then sufficiently grinding and mixing by ball miller, reacting for 6 hours at about 1400° C. under the mixture gas of N₂ and H₂.

For raw materials in Table 2, when SrCO₃, Al₂O₃, Eu₂O₃, Dy₂O₃, H₃BO₃ are respectively replaced by SrO, Al(OH)₃, Europium oxalate, Dysprosium oxalate, B₂O₃, the cyan rare-earth long-afterglow luminescent materials of similar properties are obtained.

Examples 13-17

Preparation of indigo rare-earth long-afterglow luminescent materials according to the present invention

The molar ratio of raw materials for examples 13-17 are listed in Table 3.

TABLE 3 Mole ratio of raw materials in samples (mol) Samples CaCO₃ Al₂O₃ SiO₂ Ga₂O₃ Eu₂O₃ Nd₂O₃ H₃BO₃ 13 1 1 0 0 0.01 0.02 0 14 1 1 0 0 0.01 0.02 0.1 15 1 1 0.05 0.005 0.01 0.02 0.1 16 0.6 0.6 0.6 0.03 0.006 0.012 0.6 17 0.7 1.3 0.001 0.005 0.2 0.3 1

The manufacturing method includes mixing CaCO₃, Al₂O₃, SiO₂, Ga₂O₃, Eu₂O₃, Nd₂O₃ and Boric Acid according to the molar ratio listed in Table 3 and then sufficiently grinding and mixing by ball miller, reacting for 2 hours at about 1400° C. under the mixture gas of N₂ and H₂.

For raw materials in Table 3, when CaCO₃, Al₂O₃, Eu₂O₃, Nd₂O₃, H₃BO₃ are respectively replaced by CaO, Al(OH)₃, Europium oxalate, Neodymium oxalate, B₂O₃, the indigo rare-earth long-afterglow luminescent materials of similar properties are obtained.

Experimental Example 1

Characteristics of the long-afterglow materials according to the present invention were as follows.

Each sample in Table 1-3 is excited for 10 min by means of D65 normal light source, and then its afterglow persistence is measured by means of afterglow checking apparatus provided with photomultiplier, the results are respectively shown in Table 4, 5 and 6. Sample 1 is considered as a reference value to brightness in Table 4, and sample 7 is considered as a reference value to brightness in Table 5, while sample 13 is considered as a reference value to brightness in Table 6. The luminescent spectrum of afterglow for sample 3 is shown in FIG. 1; the luminescent spectrum of afterglow for sample 9 is shown in FIG. 2, and the luminescent spectrum of afterglow for sample 15 is shown in FIG. 3.

TABLE 4 Luminance after Luminance after Luminance after Samples 10 min 30 min 100 min 1 1.00 1.00 1.00 2 14 20 22 3 13.8 21 23.5 4 6 12.5 13 5 2 3.4 2.5 6 1.8 3 3.2

TABLE 5 Luminance after Luminance after Luminance after Samples 10 min 30 min 100 min 7 1.00 1.00 1.00 8 11 15 20 9 11.2 16 21.3 10 4 10 11.8 11 3 4.5 6 12 2 4.3 5.4

TABLE 6 Luminance after Luminance after Luminance after Samples 10 min 30 min 100 min 13 1.00 1.00 1.00 14 10 12 13.4 15 10.2 12.3 14 16 4 8 9.4 17 3 5 6.3

Experimental Example 2

Water resistance of the long-afterglow materials according to the present invention was as follows.

The above resultant phosphor powder is fed into water for different times (record the dipping time), and then is dried. Each dried sample is excited for 10 minutes by means of D65 normal light source, and then its afterglow characteristic of 10 minutes after exciting is measured by means of afterglow checking apparatus provided with photomultiplier. The results of water resistance of samples in Table 1-3 are respectively shown in Table 7, 8 and 9. Sample 1 is considered as a reference value to brightness in Table 7, and sample 7 is considered as a reference value to brightness in Table 8, while sample 13 is considered as a reference value to brightness in Table 9.

TABLE 7 Luminance after dipping into water for Luminance before different times Samples dipping into water 10 h 20 h 60 h 1 1.00 1.00 1.00 1.00 2 14 4 2 1.4 3 13.8 15 25.7 33.2 4 6 7 15 18.6 5 2 8.76 16.3 19.4 6 1.8 8 13.3 18

TABLE 8 Luminance after dipping into water for Luminance before different times Samples dipping into water 10 h 20 h 60 h 7 1.00 1.00 1.00 1.00 8 11 3 2 1.1 9 11.2 13 20.3 31 10 4 6.4 12 15.8 11 3 7.6 13.5 18 12 2 7.2 12.8 17.5

TABLE 9 Luminance after dipping into water for Luminance before different times Samples dipping into water 10 h 20 h 60 h 13 1.00 1.00 1.00 1.00 14 10 3 1.3 1.1 15 10.2 14 21 30 16 4 7 12 17.6 17 3 8.2 15.8 20

The multiple rare-earth co-activated long-afterglow luminescent material according to the present invention has excellent long afterglow property and still keeps higher long-afterglow property after dipping into water for 60 hours.

While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 

1. A multiple rare-earth co-activated long-afterglow luminescent material having a chemical composition depicted by the formula aMO.bAl₂O₃ .cSiO₂ .dGa₂O₃ :xEu.yB.zN wherein a, b, c, d, x, y and z are coefficients with the ranges of 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦1, 0.0001≦z≦1; M is at least one of Ca, Sr elements and N is at least one of Dy, Nd elements.
 2. The multiple rare-earth co-activated long-afterglow luminescent material according to claim 1, wherein in the chemical composition 0.8≦a≦1.2, 0.8≦b≦2, 0.002≦c≦0.061, 0.005≦d≦0.5, 0.005≦x≦0.1, 0.02≦y≦0.5, and 0.005≦z≦0.05.
 3. The multiple rare-earth co-activated long-afterglow luminescent material according to claim 2, wherein in the chemical composition a=1, 1≦b≦2, 0.002≦c≦0.02, 0.005≦d≦0.0, 0.01≦x≦0.02, 0.05≦y≦0.3, 0.01≦z≦0.04.
 4. The multiple rare-earth co-activated long afterglow luminescent material according to claim 1, wherein the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxides or hydrates of Aluminum; Si or Ga elements result from oxides of Silicon or Gallium; Eu, Dy, and Nd result from oxides or oxalates of Europium, Dysprosium or Neodymium; and B results from oxides of Boron or Boric acid.
 5. The multiple rare-earth co-activated long afterglow luminescent material according to claim 2, wherein the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxides or hydrates of Aluminum; Si or Ga elements result from oxides of Silicon or Gallium; Eu, Dy, and Nd result from oxides or oxalates of Europium, Dysprosium or Neodymium; B results from oxides of Boron or Boric acid.
 6. The multiple rare-earth co-activated long afterglow luminescent material according to claim 3, wherein the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxides or hydrates of Aluminum; Si or Ga elements result from oxides of Silicon or Gallium; Eu, Dy, and Nd result from oxides or oxalates of Europium, Dysprosium or Neodymium; B results from oxides of Boron or Boric acid.
 7. A method for manufacturing the multiple rare-earth co-activated long-afterglow luminescent material according to claim 1, the method comprising (1) mixing raw materials sufficiently according to a following molar ratio, and (2) sintering a resultant mixture for 2-6 hours under 1200˜1500° C. at a reductive atmosphere, whereby a resultant is obtained, wherein, MO:Al₂O₃:SiO₂:Ga₂O₃:Eu:B:N=a:b:c:d:x:y:z; and 0.5≦a≦2, 0.5≦b≦3, 0.001≦c≦1, 0.0001≦d≦1, 0.0001≦x≦1, 0.0001≦y≦, 0.0001≦z≦1 are selected; M is Ca or Sr and N is Dy or Nd; sources of the said raw materials are: the Sr or Ca elements, respectively, result from carbonates or oxides of Strontium or Calcium; Al results from oxide or hydrate of Aluminum; Si or Ga elements, respectively, result from oxides of Silicon or Gallium; Eu, Dy, and/or Nd result from oxides or oxalates of europium, dysprosium or neodymium; B results from oxides of Boron or Boric acid.
 8. The method for manufacturing the multiple rare-earth co-activated long-afterglow luminescent material according to claim 7, wherein a=1, 1≦b≦2, 0.002≦c≦0.02, 0.005≦d≦0.01, 0.01≦x≦0.02, 0.05≦y≦0.3, 0.01≦z≦0.04 in a chemical composition ratio of each raw material are selected.
 9. The method for manufacturing the multiple rare-earth co-activated long afterglow luminescent material according to claim 7, wherein said reductive atmosphere is CO or H₂ gas.
 10. A use of said multiple rare-earth co-activated long-afterglow luminescent material according to claim 1 as a direction identifier for subway passengers, traffic signs, bridge identifiers, scutellate signs, border lines, walking passages, lamp posts, tunnel marks, fire control and emergency escape signs, ship decks, dock signs, and oil well signs.
 11. A use of said multiple rare-earth co-activated long-afterglow luminescent material according to claim 2 as a direction identifier for subway passengers, traffic signs, bridge identifiers, scutellate signs, border lines, walking passages, lamp posts, tunnel marks, fire control and emergency escape signs, ship decks, dock signs, and oil well signs.
 12. A use of said multiple rare-earth co-activated long-afterglow luminescent material according to claim 3 for direction identifier for subway passengers, traffic signs, bridge identifiers, scutellate signs, border lines, walking passages, lamp posts, tunnel marks, fire control and emergency escape signs, ship decks, dock signs, and oil well signs.
 13. A use of said multiple rare-earth co-activated long afterglow luminescent material according to claim 1 for dresses, aqueous inner and outer wall coatings, paints, and print inks.
 14. A use of said multiple rare-earth co-activated long afterglow luminescent material according to claim 2 for dresses, aqueous inner and outer wall coatings, paints, and print inks.
 15. A use of said multiple rare-earth co-activated long afterglow luminescent material according to claim 3 for dresses, aqueous inner and outer wall coatings, paints, and print inks. 